A seat belt retractor traditionally comprises a pressed steel U-shaped frame within which is mounted a rotatable cylindrical spool serving as a reservoir for seat belt webbing. The spool rotates about its longitudinal axis to pay-out or wind-in seat belt webbing as required, but is biased towards a webbing wound position so as to maintain the seat belt securely across the body of a vehicle occupant without slack developing. The vehicle occupant is able to move around within limits, for example, to reach a glove compartment or radio controls. However, in a crash a sensor detects a sudden deceleration of the vehicle and locks the spool against the further payout of webbing, thus securing the vehicle occupant against forward motion and preventing impact with internal parts of the vehicle.
The spool is locked by a die cast non-ferrous lockbar mounted across the open part of the arms of the U-shaped frame. The lockbar pivots in cutouts in the frame arms, into and out of its locking position. Considerable tensile forces are transmitted to the frame during a crash and to resist premature failure of the frame due to its inherent instability, thicker material and additional cross bracing are traditionally employed in the vicinity of the relevant area.
However this extra material and cross bracing results in additional weight and cost of the frame assembly. It would be advantageous to stabilize the frame without the extra material and improve the tensile load capacity with no extra parts, weight or cost.